Mine comes and goes. Not sure what is going on there, but it always comes back.

 

Just wondering if you got your vehicle within the last couple months. There are quite a number of recent posts and threads about this, I started one myself. I have to assume Subaru had a whole batch of bad sensors on hand recently. It only takes one to shut the system down. My Legacy was manufactured in July and I got it July 28. For about a month the TPMS worked properly and then stopped. On my first visit they reprogrammed the sensors into the unit and that worked for 2 weeks. Second time they realized one sensor, left rear, was giving erratic readings which they said was indicative of a failing battery. They replaced it about 3 weeks ago now and it’s been fine.

Take it in and mention that you’re aware of others with the same problem. Again I’m guessing that there was a bad batch and Subaru needs to know and get that information to the dealers.

 

I took it back to the dealers yesterday. I was a little spooked by the first person who came out and asked what the problem was. I told him and he said they only show the pressure if a tire is low. I had to set him straight on that. Then he checked the tire pressures and didn't know that the fronts have 2# more than the rears. He kind of wanted to argue with me about. My wife stepped in and told him that I had read the manuals and am usually right. I then showed him the chart inside the drivers door. I also had to inform him that you have to get up to 20 mph before they start to work. That took care of that. He needs some training. They took the car back into the shop, I was a little worried about not staying with it but we went into the waiting room. About a half an hour later we were informed that they had to reset all the monitors, and that was the first time they ever had to do that. I just hope the mechanic was smarter than the first guy we talked to. In the end they are all working for now.

 

About a half an hour later we were informed that they had to reset all the monitors,

I believe you had stated that the TPMS was displaying pressures previously. Mine had for the first month I had the car then that one, apparently, bad sensor acted up. They reset mine as well, or reprogrammed them as I was told, this doesn’t last because the problematic sensor will cause the system to fail again. It lasted about 2 weeks. So keep an eye on it, odds are you’ll be back at the dealer. I do think Subaru had a bad batch of sensors.

 

Like my car, they probably didn't PDI it correctly to begin with. Another dealer took care of it and I haven't had trouble since.

 

Schrader is Subaru's main supplier of sensors. And although there are dozens of variations on the basic part number 28103xxxxxx, there are really only 2 basic flavors. And within those 2 classes (315 MHz for most older, 433 for most newer), the various series numbers will work interchangeably. Meaning: Dealers really don't have to stock a lot of parts to satisfy demand.

UNLESS, as you said, a bunch of bad parts left the assembly line, and dealers have gotten swamped with customers needing replacement parts that's wiped out their stock.

 

I’ve also got no TPMS reading, and no yellow alert light. Built in August and purchased two weeks ago, already back to the dealer once for alignment, realized the next day the TPMS wasn’t working. Guess it’s time for another visit already. Sigh.

 

Unless you want to make at least two separate visits make certain they have them in stock and that when they have your car they check for the defective one. There will be at least one. Too many people are posting about this - many will not be checking the system so could remain unaware for weeks - for me not to conclude that this is the result of defective sensors that Subaru was installing in the July and later cars.

 

Just to avoid confusion for anybody that might expect to see tire pressure readings as soon as they turn on the car... please keep in mind that it may take several minutes of driving at speeds over 20mph before the reading appears on the dash. I know the 20mph part was mentioned earlier in this thread, but not the several minutes part. Obviously there are legitimate TPMS issues in some cars, but this may save some grief for those that might expect to see the tire pressure reading immediately upon starting the engine or as soon as they hit 20mph.

 

Yep, this is so true, and for good reason, as you'd see a pretty different reading, if they were cold (and perhaps a really skewed one, if it were REALLY cold out).
I do think they should put a little "warming up" type of message (not that exact message, but I'm sure someone could get clever with it), instead of the non-reads, which is confusing, in the warmup-interim.

 

Twice I have called whoever could tell me if they had the parts, and there was no answer. Twice I left my name and phone number and never got a call back.

 

It's not really a 'warming up' thing as much as a 'waking up' issue.

That little coin cell battery has to last 7-10 years. To do that, your sensors broadcast a very short pulse, low power signal, and only when needed. Whenever the tires sit still for long, the sensors shut down and go to sleep.

Normal wake-up is done by an integral 2 axis accelerometer. Only after wheel rotation exceeds a certain speed will broadcasting begin. If too many signals are received in quick succession, some will be ignored, and the system will wait for the rejected signals to be broadcast again. Depending on firmware, that could take several more minutes. So yes, it can take several minutes to get a reading. If all signals aren't received and logged in within around 20-30 minutes, the system should log a fault and show a blinking or solid light (depends on nature of fault).

If pressure is really low in the tire(s), the sensor should go into hyper-broadcast mode, and shout out a warning.

 

It's not really a 'warming up' thing as much as a 'waking up' issue.

That little coin cell battery has to last 7-10 years. To do that, your sensors broadcast a very short pulse, low power signal, and only when needed. Whenever the tires sit still for long, the sensors shut down and go to sleep.

Normal wake-up is done by an integral 2 axis accelerometer. Only after wheel rotation exceeds a certain speed will broadcasting begin. If too many signals are received in quick succession, some will be ignored, and the system will wait for the rejected signals to be broadcast again. Depending on firmware, that could take several more minutes. So yes, it can take several minutes to get a reading. If all signals aren't received and logged in within around 20-30 minutes, the system should log a fault and show a blinking or solid light (depends on nature of fault).

If pressure is really low in the tire(s), the sensor should go into hyper-broadcast mode, and shout out a warning.

Why would these sensors use batteries? Seems like they could generate enough electricity by having a little magnet go up and down inside a coil every time the wheel turns. Batteries wear out.

 

Well had the Outback back in again because the tpms wasn't working again. This time they told me that it is saying I have been driving on to rough a road????? I have only been on the highways, and local blacktop roads., all in good condition. Never been offroad. The person said that I need to drive on better roads.... Hate to see what would happen if I take it off road. Will the engine fall out?? They said there is nothing they can do because there is nothing wrong?? Maybe if I keep it parked in the garage it might be OK, but there is a small crack in the concrete floor. Told them I'll see them again in a week or two. I don't know where to go from here. Is there a Corporate number I can call to get something done??

 

Call the customer line. Create a case number and go to another dealer. Subaru has bad sensors in the recent cars and they need to step up.

 

Do you have a different dealership?
Those guys sound like they don't know much.

Sent from my SM-G960U using Tapatalk

 

I had a similar issue with my new one, the tyre pressure monitors worked when I got the car, then stopped at some point.

I went to check the pressure manually with a pressure gauge, and then immediately when I got back in the car the sensors were working properly again.

Figured that moving a little bit of air over a couple of the sensors kicked them back into life somehow.

 

I can only think that Subaru will be issuing a service bulletin on this soon. Too many posts here, all from recently produced vehicles, mine was a July manufacture and that seems to be quite common - July or later. I’ve spoken to a few new owners of Outbacks in my area and all but one has had the issue And that one had only checked the pressures when she took delivery of the car but not since. They just used a bad batch of sensors this summer. Only takes one to bring down the system.

 

Those with problems need to seek out a friend or co-worker, or even a local tire shop that could walk around and ping each tire and see if the sensors respond. I've done it for folks at work that have had issues (other vehicles, pre-COVID) and helped them identify which sensor was iffy (no response, slow to respond).

 

I think the bigger problem here is that these things are made as-cheaply-as-possible, to last just long enough for a warranty period, or similar.
If you multiply these sales, from some manufacturer by 4-5/car, you can quickly see how the economy-of-scale is a BIG deal for them, say if they save $0.03/valve, but have to warranty one every 100 or so, they're still ahead 3x...

 

When first introduced, the prediction was 5-7 years life. The limited data I've seen indicates they are going 10 years, or more. You don't hear about a lot of failures. It would be hard to improve upon the lifespan or cost of the product with an electromechanical generation system vs the existing coin cell battery design.

 

Yeah, our 2013 is doing okay, with the originals (knock on metal/rubber now that I've posted this).
I do wish they'd figured out a way to replace the coin cells, via the valve stem or similar, instead of having to remove the tires, it'd be a TON easier to fix these random-battery-issues, if you could just jack up one corner, pull the battery out via the valve-stem, and replace (I'd do this hands-down, before scheduling a service-appt).

 

I have an air compressor that took the psi reading on all but one tire. Now it won't take a reading on all four and i can't fill the with the air compressor. I have to go to a shop to use theirs.

 

The chuck on your compressor has a post in the center that has to depress the central 'schrader' valve core in order to take a reading or to fill efficiently. I've had chucks where the center post moved inward and would no longer work on a car or bicycle.

 

Yeah, it's worth spending a few extra $$$, for a decent brass-construction chuck, from NAPA, or similar, it'll be a lifetime deal, in most cases...
Buying cheap-o pneumatic stuff is almost always a bad move overall, IME, it's way better to buy someone's lightly-used tool, on auction, or similar.

Having presta on ALL my bike tires, since the late 80's (yeah, I'm a ex-racing bike-geek, of sorts), I don't have any of those post-issues, in that department ;-]

 

8 days after they reset the sensors they stopped working again. This is the third time. Last evening it was the wifes birthday and we went about 30 miles to a Cracker Barrel. The tire pressures were showing properly when we went in. When we came out they didn't work anymore. Called the dealership where we got the car, and talked to the top guy in the service dept. Explained to him about the problem, and that I was getting tired of driving all the way up there, and that they couldn't seem to fix this simple problem. They are sending out a guy with a loaner car, and he will drive ours back to the shop, and hopefully now they will figure it out.

 

Curious if any stealership has changed out anyone's TPMS control module. It's only a $100 part.

 

Since TPMS is a federally mandated safety feature, if they can't fix your TPMS after 3 tries, depending on your State law, it may qualify for lemon law. I'm not "suggesting" this as an outcome, but just something to consider if you need more leverage or if for whatever reason they can't figure it out.

 

Being a Forester owner also, I'm working with a 2020 owner who received a Winter Package from TireRack with new sensors that won't work properly. TireRack typically installs Schrader sensors, pretty much twin sisters to the units that Subaru is using.

The OP on this particular thread also owns an Autel TS508, so I coached him on uploading (registration) codes, and then using Advanced Diagnostics to capture DTC's when his display went blank. He retrieved two sensor codes (C2121 & C2122), but also C2921, something I've never seen before and could not find in the service manual for my 2018 Forester (which still uses the old 315 MHz system). The Forester went to the full display and 433 MHz sensors for 2019.

I checked into other SOA documentation, and got a "hit" with Subaru Tech Tips, April 2020 edition. Not good. There's a 3 page deep tech description of getting C2121 thru C2124, followed by C2921. It's a communications error, sometimes caused by either a registration error (uploading the hex ID of the new sensors) which could be an Autel tool thing, or the system not seeing certain expected changes in broadcast data from the sensors (like incremental increase in temp or pressure as you drive indicating "live" data) over time. It might be an attempt by the vehicle to ensure real live data, and maybe not 'spoofed' or canned data, or a "stuck" sensor that just keeps repeating stored data without sampling the actual conditions first (a sensor failure).

How I would love for someone with the blank display issue to demand to know more from the Service Department about exactly what DTC codes they are retrieving and what SOA thinks is going on!

 

Being a Forester owner also, I'm working with a 2020 owner who received a Winter Package from TireRack with new sensors that won't work properly. TireRack typically installs Schrader sensors, pretty much twin sisters to the units that Subaru is using.

The OP on this particular thread also owns an Autel TS508, so I coached him on uploading (registration) codes, and then using Advanced Diagnostics to capture DTC's when his display went blank. He retrieved two sensor codes (C2121 & C2122), but also C2521, something I've never seen before and could not find in the service manual for my 2018 Forester (which still uses the old 315 MHz system). The Forester went to the full display and 433 MHz sensors for 2019.

I checked into other SOA documentation, and got a "hit" with Subaru Tech Tips, April 2020 edition. Not good. There's a 3 page deep tech description of getting C2121 thru C2124, followed by C2921. It's a communications error, sometimes caused by either a registration error (uploading the hex ID of the new sensors) which could be an Autel tool thing, or the system not seeing certain expected changes in broadcast data from the sensors (like incremental increase in temp or pressure as you drive indicating "live" data) over time. It might be an attempt by the vehicle to ensure real live data, and maybe not 'spoofed' or canned data, or a "stuck" sensor that just keeps repeating stored data without sampling the actual conditions first (a sensor failure).

How I would love for someone with the blank display issue to demand to know more from the Service Department about exactly what DTC codes they are retrieving and what SOA thinks is going on!

There was also a recent TSB issued for the TPMS and DTC2921..

05-78-20 Technical Service Bulletin
DTC C2921 ID Registration Error and Bit Translation Table for Use in Tire Pressure System (TPMS) Diagnostics
Oct 13, 2020

Probably more of the same stuff that’s in that techtips article.

 

Got our car back Thursday. They said they had to order 4 tpms units, and then replaced all four. Might take a couple of weeks to see if they continue working. Got my fingers crossed. Maybe mentioning the lemon law might have helped a little.

 

So far so good!!!!

 

Read a lot of this thread looking for the Canadian flag cause Subaru’s in Canada don’t come with TPMS! One of a number of irritants that Subaru has. Likely will go back to a Ford next time!

 

I’ve never seen by TPMS like this. It’s been like this for about 50 miles and several key cycles. Normally they are a little Dash lines on each side before it acknowledges the actual pressure. Now there is nothing. Is this a known issue?

 

It means one or more of the tire sensors are defective, usually a battery going bad or dying. If one goes out the system just reverts to that display. That’s how it was with mine and others on this forum. The dealer can find out which one(s) it is and replace it.